The present invention relates to a power-on-reset system for use in microcontroller-based products. More particularly, the present invention relates to a multiple phase power-on-reset device and technique for facilitating the reliable powering on and resetting of the microcontroller.
The demand for higher performance, microcontroller-based products for use in communication and processing applications continues to increase rapidly. As a result, microcontroller-based product manufacturers are requiring for the components and devices within these products to be continually improved to meet the design requirements of a myriad of emerging audio, video and imaging applications. These microcontroller-based products use various types of processors, for example, general purpose microprocessors for controlling the logic of various digital devices, such as clock radios, microwave ovens, digital video recorders and the like, and special purpose microprocessors, such as math coprocessors for mathematical computations, or digital signal processors used in manipulating various types of information, including sound, imaging and video information.
The microcontroller typically includes a central processing unit (CPU) core for the processing functions, and a bus interface for communication with the various memory devices as well as external or other peripheral devices. For the storage of data, the microprocessor can include various types of memory. For example, the CPU for the microcontroller may include Random Access Memory (RAM) as well as Read-Only Memory (ROM). In addition, the microcontroller can also include flash memory which can be erased in blocks and reprogrammed one byte at a time.
For the transmitting and receiving of data between various devices and components, microprocessors and other devices utilize various types of serial interfaces. One such type of interface typically used is the serial peripheral interface (SPI). In addition, for the temporary storage of data, for example, to permit the microprocessors to manipulate the data before transferring the data through the SPI to another device, the microprocessors generally utilize one or more buffers. These buffers are configured with the SPI""s to enable the processors to transmit and receive data to and from the buffers as needed in an application.
When a microprocessor or other electronic device is powered on, the power supply generally ramps up to a steady supply voltage level. Some power supplies ramp up faster than others, and generally, the more quickly a power supply ramps up the more expensive the power supply is to purchase. Until such power supplies reach a desired voltage level, individual circuits and devices as a whole behave unpredictably. For example, some devices may begin to work properly at a lower voltage than other devices. Some devices may also begin to work properly at less than their rated voltage levels. With only some of the components working properly, the whole system may behave unpredictably. In addition, devices operating at less than the rated voltages are less reliable. Therefore, circuits are typically held in a reset mode until a minimum voltage level has been reached.
Furthermore, if during normal operation, the power level drops below this minimum voltage level, for example when a laptop""s battery begins to run out of power, the circuits are also placed in reset mode. This minimum voltage level is known as the brown out reset voltage level. The brown out reset voltage level varies among different digital devices and even varies among different applications for the same integrated circuit (xe2x80x9cICxe2x80x9d) device. Furthermore, the time to ramp up to the brown out reset voltage for a particular IC device may change if the power supply is replaced over the life of the IC device. Thus, it is desirable to be able to set the brown out reset voltage level and to be able to reconfigure the voltage level for various applications from time to time.
If the reset mode is released for even a short period of time, before the brown out reset voltage level is reached, the entire device may fail, crash, or be laden with potential errors that could cause the device to perform unpredictably at some later point in time. Therefore, it is desirable to have accurate and reliable power-on-reset devices. Furthermore, it is also desirable to turn on the device as quickly as reliably possible.
Previous attempts to provide a predictable power on for an IC device have included the use of fuses to set the brown out reset voltage level. However, this approach has various drawbacks as fuses are relatively unreliable. For example, it is difficult to test whether the desired fuses are blown, partially blown or not blown at all. Furthermore, systems that are programmed by blowing selected fuses are not reconfigurable once the system is programmed. In addition, in systems that are programmed via fuses, a discrete number of fuses are used. Thus, the voltage levels available to be set as the brown out voltage level are limited to discrete voltage levels with an error potential of half the voltage difference between successive possible voltage levels. Although some approaches have included additional fuses to reduce this source of error, these approaches generally require further IC space and material, increased product size, and the increased probability of device failure by adding additional fuses that may fail.
In addition, prior attempts to provide power-on-reset control have been rudimentary. Prior attempts, for example, do not lend themselves to providing intelligent functions upon the occurrence of particular conditions. Moreover, prior attempts may not be easily reprogrammed to account for system changes.
Accordingly, a need exists for an improved system for powering on an IC device that solves the above problems. In addition, a need exists for an improved system for powering on an IC device that provides the ability to set and reconfigure the brown out voltage level, with accuracy, for different configurations. Furthermore, a need exists for a more reliable powering on of an IC device. Also, a need exists for power-on-reset methods that allow the use of less expensive power supply devices while still providing quick power on reset. In addition, a need exists for an improved system for powering on an IC device that is compact and uses less surface area on a chip.
The method and device according to the present invention addresses many of the shortcomings of the prior art. In accordance with one aspect of the present invention, a method and device is provided which powers on an integrated circuit device by holding all of the integrated circuits of a microcontroller in a reset mode until a subset of circuits can be reliably released, wherein the subset of circuits is then used to determine when to release the rest of the circuits of the integrated circuit device. In accordance with an exemplary embodiment of the present invention, a two phase process is provided where, during a first phase, all circuits are held in reset mode until a sufficiently high voltage level allows for powering on of a system reset device which, during a second phase, continues to hold the remaining circuits in reset mode until the current voltage level reaches a reprogrammable brown out level. In addition, during normal operation, when the voltage drops below this programmed brown out voltage level, the device reenters the second phase and remains there until the voltage goes above this level. In accordance with another aspect, a reprogrammable enable signal is provided allowing reprogrammable bypass of the second phase voltage level checking. In another exemplary embodiment of the present invention, flash memory is used to hold the reprogrammable brown out level and enable.
In accordance with another aspect of the present invention, the reprogrammable brown out voltage level and brown out enable creates a power-on-reset apparatus that can be flexibly adaptable to changing integrated circuits. In other aspects, the reprogrammable brown out level is testable, more accurate and more reliable than fuse type power-on-reset devices. In accordance with a further aspect, the two phase process provides additional power on functionality. In another aspect, the power-on-reset provides a time efficient power-on-reset process which is also space efficient.